Apparatus for coating woven or nonwoven webs

ABSTRACT

The invention consists of an apparatus and process for applying a coating to a woven or nonwoven web. The apparatus is comprised of a casting box for holding a coating material, an arrangement of slotted, rotating and nonrotating tubes for supplying a moving stream of coating composition into a pressure balancing zone above the web, a means for supplying the coating composition to the tubes, and a doctor blade suitably disposed above the web to achieve a coating of uniform thickness. In the process, the movement of the coating composition relative to the web is in the form of periodically recurring, parallel lines, intersecting the center axis of the web at a constant angle of 0*&lt; Alpha &lt;90*. By utilizing the apparatus and process disclosed herein, a uniform coating, free of color bands or strips, can be achieved.

1111 States Patent Clemens Neuhaus; Klaus Boehme, both of Erlenbach;Hermann Gutermuth, Kleinwallstadt, all of lnventors Germany Appl. No.848,038 Filed Aug. 6, 1969 Patented Dec. 21, 1971 Assignee Glanzstofi AGWuppertal, Germany Priority Aug. 6, 1968 Germany APPARATUS FOR COATINGWOVEN 0R NONWQVEN WEBS 3 Claims, 4 Drawing Figs.

lnt. Cl B05c 3/00 lField of Search 1. 1 18/410,

4l3,4l5,414,4l 1,407, 259; 18/13 P, 15 F, 15 R [56] References CitedUNITED STATES PATENTS 1,667,408 4/1928 Allen 118/415 X 2,796,146 6/1957Hersey etal.. 118/410 UX 3,083,685 4/1963 Colgan 118/410 3,419,9341/1969 Lovett 18/15 F X Primary Examiner-John P. MclntoshAttorney-.lohnston, Root, OKeeffe, Keil, Thompson &

Shurtleff ABSTRACT: The invention consists of an apparatus and processfor applying a coating to a woven ornonwovcn web. The apparatus iscomprised of a casting box for holding a coating material. anarrangement of slotted, rotating and nonrotating tubes for supplying amoving stream of coating composition into a pressure balancing zoneabove the web, a means for supplying the coating composition to thetubes, and a doctor blade suitably disposed above the web to achieve acoating of uniform thickness. In the process, the movement of thecoating composition relative to the web is in the form of periodicallyrecurring, parallel lines, intersecting the center axis of the web at aconstant angle of 0 a 90. By utilizing the apparatus and processdisclosed herein, a uniform coating, free of color bands or strips, canbe achieved.

PAIENTEDflEmm $628503,

SHEU 1 OF 2 INVENTORS: CLEMENS NEUHAUS KLAUS BOEHIVIE HERMANN GUTERMUTHATT'YS PAIENIEB mm m SHEET 2 OF 2 INVENTORS: CLEMENS NEUHAUS KLAUSBOEHME HERMANN GUTERMUTH APPARATUS lFOllt COATING WOVEN on nonwoven wensBACKGROUND OF THE INVENTION This invention relates to an apparatus forapplying a coating to a woven or nonwoven web and more particularly toan apparatus for applying a uniform coating free of color strips.

There are a number of existing processes for coating woven or nonwovenwebs. The choice of a particular process depends upon the consistency ofthe coating composition, on the thickness of the application, and on thetype of carrier material. Thus, for example, thin solutions can beapplied by the reverse-roll-coat process; while thick solutions, pastesor gels, are generally applied by the brushing (spreading) process. Thespreading process is the more complex one having a greater degree ofvariation. Coating compositions, including pastes and gels, can becombined with color pigments or be dyed using soluble dye materials toachieve a desired effect. The spreading process, which includes theapplication of coating materials by means of roller wipers, rubberblanket wipers, or support wipers, can be used to achieve a coating ofuniform thickness, but it is frequently difficult, using this process,to obtain a uniform color over the entire width of the material. In theconventional spreading processes, longitudinal stripes form and becomevisible because of the more or less great differences in colorintensity. So far, no satisfactory explanation has been given for theoccurrence of these variations in color. One example of a coatingcomposition which is difficult to handle and produces the aforementionedcolor stripe, is polyurethane gel. The polyurethane solid content lies,as a rule, between and 40 percent by weight.

One of the conventional methods for applying a polyurethane gel coatingconsists of supplying the gel over a stationary feed device in front ofa doctor blade. In this process, however, a rotating bulge of gelmaterial occurs in front of the doctor blade during the spreadingprocess. After passing the doctor blade, the web has, as a rule, asmooth but nonhomogeneously colored covering layer which is permeatedwith longitudinal stripes. In addition, air is often imbedded by therotating bulge thereby producing a faulty covering layer.

The streakiness in color cannot be avoided either by reducing or byenlarging the bulge. Nor is it possible in the conventional process toachieve any substantial improvement of the covering layer by applyingthe gel through a stationary distributor tube situated in the rotatingbulge. Similar attempts to apply the coating composition through a tubewith a longitudinal slit or with a row of holes have likewise failed toachieve the desired results.

Other attempts to limit or reduce the bulge by utilizing a casting boxinstalled on the doctor blade, into which the gel is supplied atdifferent places, have failed to achieve a covering layer free ofstripes. This approach has shown, however, that by engaging a castingbox in front of the doctor blade, it is possible to obtain animprovement in the smoothness of the covering layer because of theabsence of air bubbles.

Finally, attempts have been made to mount a traverse device above thecasting box ahead of the doctor blade to convey the gel downwardlythrough a tube into the casting box. This process has proven to be oflittle advantage, since the reciprocating back and forth of the tubecauses air bubbles in the gel resulting in nonuniform coating layers.

SUMMARY OF THE INVENTION It is, therefore, an object of the presentinvention to provide an improved coating apparatus for applying astripe-free colored covering layer on woven or nonwoven webs.

It is a further object of the present invention to provide coatingapparatus which will prevent the occurrence of air bubbles in thecoating composition thereby achieving a more uniform coating layer.

In a preferred embodiment of the invention, a woven or nonwoven web isarranged to pass over a roller means. A wiper or doctor blade isdisposed above the moving web. A

casting box is arranged in front of the doctor blade and above themoving web such that the casting box and the doctor blade form anenclosed vessel for holding a quantity of coating material. A doubletube, having an inner tube and an outer tube, is mounted in the castingbox above the moving web. An outer tube having a straight slot facingthe roller is attached in a fixed nonrotating position in the castingbox. The straight slot extends the full width of the casting box. Theinner tube is rotatably mounted in the outer tube and is connected by ashaft means to a source of driving power. A spiral slot, which alsoextends the full width of the casting box, encircles the inner tube andmakes at least one turn around the circumference of the inner tube. Inthe preferred embodiment of the invention, the spiral slot in the innertube covers the width of the casting box in two turns. The inner spaceof the inner tube is connected to a source container for the coatingcomposition.

Since the inner tube contains a spiral slot which makes at least oneturn around the circumference of the inner tube, and since the outertube has a straight slot, there will be one or more places along thelength of the tubes where the spiral slot and straight slot willoverlap. The points of overlap are called feed places since the coatingcomposition can pass from the space interior to the inner tube throughthe overlapped slots into the vessel formed by the casting box and thedoctor blade.

The use of the double tube as a rotating gel distributor makes possiblethe construction of a compact, closed casting box in which the staticpressure in the gel can be increased by introducing an inert gas, underpressure, into the casting box above the coating composition.

Inside the casting box, the space lying between the feed places and themoving web is designated as a pressure balancing zone. The pressurebalancing zone is utilized to diffuse the orifice pressure in thecoating composition at the feed places to avoid any streakiness whichmight be caused by pressure variations. In the case of polyurethanegels, the spacing between the outer tube and the roller lies generallybetween 0.5 centimeters and 5 centimeters. With this spacing, asufficiently large pressure balancing zone is created. Depending uponthe viscosity conditions, however, this spacing can be larger orsmaller.

During the coating process, the uncoated web is conveyed and supportedon a roller and passed beneath the casting box whereupon the coatingcomposition is applied to the web. After passing through the pressurebalancing zone, the coating composition is wiped by the doctor bladeonto the web in a known manner. The coated web emerges under the doctorblade, the height of which is suitably adjusted to achieve a coatingofuniform thickness.

The rotation of the inner tube causes the overlap (feed place) of thespiral slot and straight slot to move from one side of the casting boxto the other. This movement of the feed place relative to the movementof the web may be graphically depicted as a series of recurrent parallellines (relative movement lines) intersecting the central axis of the webat an angle (I, wherein 0 a Since the relative movement of the feedplaces with respect to the moving web is not a zigzag movement, as inthe conventional processes using traverse motion feed tubes, it has beenpossible to achieve a stripe-free coating layer. In order to achievethis stripe-free coating, it appears essential that the angle a begreater than 0 but less than 90, whereupon the angle between therelative movement lines and the doctor blade is an acute angle whichalways remains constant. Under these circumstances, any occurrence ofobliquely running stripes in front of the doctor blade will beeliminated and the web leaving the doctor blade will have a stripe-freecovering layer.

Preferably, the tangent. angle of a lies between 1 and 8. This meansthat the angle between the relative movement lines and the central axisof the web lies between 45 and 82. In this range, the spacings betweenthe parallel relative movement lines are relatively small and theresolving capacity of the doctor blade is especially good. Best resultsappear to be obtained when the tangent of the angle a lies between 3 and4; i.e., when the angle lies between 72 and 76.

In choosing the number of turns of the spiral slot formed on the innertube, it should be noted that the angle a is dependent upon the velocitywith which the web passes through the apparatus, on the rotational speedof the inner tube, on the width of the endless web, and on the number ofturns of the spiral slot on the inner tube. If the width of the web andits velocity are held constant, the stripes in the covering layer willbe avoided with equal effect if the quotient of the turning speed of theinner tube to the number of turns of the spiral slot on the inner tubeis constant. As previously stated, the inner tube is provided with atleast one slot covering, in spiral form, the entire casting box width inat least one turn. Of course, it is also possible to use multicourseslots, i.e., parallel slots. If multicourse spiral slots are employed,then it is theoretically no longer necessary that the number of turns ofthe spiral slot on the inner tube has to be an integral number greaterthan or equal to one. It is expedient, however, in order to avoidoverlapping of the zones covered, to utilize an integral number of turnsof the spiral slot on the inner tube and, in the case of multicourseslots, to keep the number of turns equal.

The preferred embodiment of the invention described herein hassubstantial advantages over the known or conventional coating machines.In particular, the absence of a reciprocating traverse and the presenceof a casting box brings about the following important advantages:

First, a reduction of the boundary layer between air and coatingcomposition is achieved; second, it is possible to achieve a coatinglayer which has few faults; and third, it is possible to subject thecoating composition to a constant static pressure so that constantconditions of application can be achieved.

Further features and advantages of the invention will become morereadily apparent from the following detailed description of a specificembodiment of the invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS fig 1 is a side elevation, partiallyin section, of one embodiment of the invention;

FIG. 2 is a section view taken along line 2-2 in FIG. 1;

FIG. 3 is a schematic representation of a web passing through the geldistributor embodied in the present invention showing the time andspatial relationships between the gel feed places and the moving web;and

FIG. 4 is a schematic representation showing the time and spatialrelationship between a gel feed tube in traverse motion and a movingweb.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS. 1 and 2,casting box 1 is arranged in front of wiper or doctor blade 2 andimmediately above roller 5. Outer tube 3 is rigidly and nonrotatablymounted as shown in casting box 1. Slot 4, which extends approximatelythe width of casting box 1 and is situated as shown in tube 3, isoriented directly above and facing roller 5. Sleeves 11, seal off tube 3as it passes through casting box 1. Inner tube 6 which is rotatablymounted in outer tube 3, is connected through shaft 14 to a drive means(not shown). Spiral slot 7, situated as shown on inner tube 6, extendsthe width of casting box 1 and is arranged to make at least one turnaround inner tube 6'over the width of casting box I.

As indicated herein, slots 4 and 7 extend the width of casting box 1.This is intended to mean that normally the length of these slots can beidentical with the width of casting box 1. It is, of course, possible tomake the slots somewhat shorter than the casting box width if that isdesired. The width of web 12 on the other hand is normally somewhatgreater than the length of slot 4. In the case of the apparatusrepresented in FIG. 1, spiral slot 7 forms two turns over the width ofcasting box I. As used herein, a turn is defined as a spiral curve whichencloses the circumference of inner tube 6, and therefore, in axialprojection, includes one rotation through an angle of 360.

A viscous coating composition 15 is pumped from container 27 throughtube 25 into gel tube 9 in the direction designated by the arrow A shownin FIG. 1. The ends of tubes 3 and 6 extend as shown beyond castingbox 1. Viscous coating composition 15 is conveyed from gel tube 9through annular space 16 in outer tube 3 and slot opening 17 inner tube6 into inner space 8 of tube 6. The places where slots 4 and 7 covereach other are designated feed places 23. Coating composition 15 isdelivered from inner space 8 through the feed places 23 into pressurebalancing zone 19 which lies between outer tube 3 and roller 5.

Uncoated web 12, moving in the direction indicated by arrow C" in FIG.2, passes between casting box I and roller 5. During operation of theinvention, casting box 1 is partially filled with coating composition asshown in FIG. 2. Casting box 1 is disposed above the uncoated web 12such that none of the coating composition 15 wells forth under the sideof casting box 1 lying opposite wiper or doctor blade 2. With castingbox 1 so disposed, no rotating bulge of coating composition 15 will formin the area 18 between casting box 1 and uncoated web 12. As theuncoated web 12 passes through the pressure balancing zone 19, coatingcomposition 15 is applied, and coated web 13 emerges under wiper ordoctor blade 2 in the direction indicated by arrow D in FIG. 2. Doctorblade 2, which performs a wiping operation, is arranged above coated web13, so as to obtain a uniform coating thickness.

In order to achieve pressure balancing and to generate sufficientlygreat static pressure, an inert gas is introduced through connection 10in the direction indicated by arrow B." This gas acts against thesurface 26 of coating composition 15 to increase the pressure in thecoating composition.

FIG. 3 is a schematic representation showing the relative movementbetween feed places 23 and the centerline of moving coated web 13. Thisrelative movement can be represented by a series of parallel straightlines 20 which intersect the centerline 24 of web 13 at a constant anglea where 0 a 90. Of the three feed places 23 shown in FIG. 3 at least twomay be utilized to supply coating composition 15 into the pressurebalancing zone 19. Once during each revolution of inner tube 6, however,three feed places can be utilized namely, at both ends and in the middleof slot 4.

FIG. 4 is a schematic representation, included for comparison purposeswith FIG. 3, showing the relative movement, in a conventional wipermachine, between a feed place 22 in traverse motion and a web 13. Thisrelative movement can be represented by a zigzag line 21 which passesthe center line 24 alternately at an angle B less than 90 and a greaterthan 90.

EXAMPLE A nonwoven carrier material (web), centimeters in width, issupplied to the apparatus described in detail in FIGS. 1 and 2, at avelocity of 2 meters per minute. Inner tube 6 has a two-turn spiral slot7. The feed places 23 will have a separation of 40 centimeters.

The widths of slots 4 and 7 are 3 millimeters. The inner tube 6 rotatesat 10 rpm. Consequently, I revolution requires 0.1 minutes (6 seconds).During this 6 second period, feed places 23 will move along straightslot 4 by 40 centimeters. During the same interval, 20 centimeters ofweb 13 move past slot 4.

Accordingly, the tangent of the angle a between the line 20, whichrepresents the relative movement between feed places 23 and web 13, andthe centerline 24 of web 13, is two. The angle a is, therefore, about64. Under these conditions, a covering layer consisting of a coatingcomposition 15 made up of a polyurethane gel having a solid substancecontent of 20 percent by weight, will be completely free of stripes.

While the foregoing description has referred to a specific embodiment ofthe invention, it will be apparent that many modifications andvariations may be made therein without departing from the spirit andscope of the invention.

We claim: 1. Apparatus for applying a stripe-free coating to a woven ornonwoven web comprising in combination:

a. a roller means disposed below said web for conveying and supportingsaid web;

b. wiper means disposed above and substantially perpendicular to thecenterline of said web;

c. casting box means arranged forward of said wiper means;

d. a first tube means rigidly mounted in said casting box means, saidfirst tube means arranged generally above said web;

. a straight slot in said first tube means, said slot being orienteddownwardly toward said web and extending the full width of said castingbox;

l. a second tube means rotatably disposed in said first tube means, saidsecond tube means extending the full width of said casting box;

g. at least one spiral slot situated in the circumference of said secondtube means and extending substantially the full width of said castingbox, said spiral slot executing at least one complete turn around thecircumference of said second tube means;

h. a cylindrical inner space disposed in said second tube means;

i. a container for storing said coating composition;

tion:

j. means for conveying said coating composition from said container tosaid cylindrical inner space;

k. shaft means operatively associated with said second tube means; and

i. drive means connected to said shaft means for rotating said secondtube means.

2. Apparatus in accordance with claim 1 comprising in addia. cover platemeans engaging the upper edges of said casting box means;

b. a source of pressurized inert gas; and

c. means for conveying said gas into said casting box means at a pointabove the surface of the coating composition contained in said castingbox.

3. Apparatus in accordance with claim ll wherein said means forconveying said coating composition from said container to saidcylindrical inner space comprises in addition:

2. Apparatus in accordance with claim 1 comprising in addition: a. coverplate means engaging the upper edges of said casting box means; b. asource of pressurized inert gas; and c. means for conveying said gasinto said casting box means at a point above the surface of the coatingcomposition contained in said casting box.
 3. Apparatus in accordancewith claim 1 wherein said means for conveying said coating compositionfrom said container to said cylindrical inner space comprises inaddition: a. pipe means communicating with said container; b. annularchannel means disposed in said first tube means and communicating withsaid pipe means; and c. slotted openings disposed in said second tubemeans and communicating with said annular channel means and saidcylindrical inner space.